学习目标
学习openGauss收集统计信息、打印执行计划、垃圾收集和checkpoint
课程学习
连接数据库
#第一次进入等待15秒
#数据库启动中...
su - omm
gsql -r
1.准备数据
Create schema tpcds;
CREATE TABLE tpcds.customer_address
(
ca_address_sk integer NOT NULL ,
ca_address_id character(16),
ca_street_number character(10) ,
ca_street_name character varying(60) ,
ca_street_type character(15) ,
ca_suite_number character(10) ,
ca_city character varying(60) ,
ca_county character varying(30) ,
ca_state character(2) ,
ca_zip character(10) ,
ca_country character varying(20) ,
ca_gmt_offset numeric(5,2) ,
ca_location_type character(20)
);
insert into tpcds.customer_address values
(1, 'AAAAAAAABAAAAAAA', '18', 'Jackson', 'Parkway', 'Suite 280', 'Fairfield', 'Maricopa County', 'AZ', '86192' ,'United States', -7.00, 'condo'),
(2, 'AAAAAAAACAAAAAAA', '362', 'Washington 6th', 'RD', 'Suite 80', 'Fairview', 'Taos County', 'NM', '85709', 'United States', -7.00, 'condo'),
(3, 'AAAAAAAADAAAAAAA', '585', 'Dogwood Washington', 'Circle', 'Suite Q', 'Pleasant Valley', 'York County', 'PA', '12477', 'United States', -5.00, 'single family');
–使用序列的generate_series(1,N)函数对表插入数据
insert into tpcds.customer_address values(generate_series(10, 10000));
2.收集统计信息
–查看系统表中表的统计信息
select relname, relpages, reltuples from pg_class where relname = ‘customer_address’;
—使用ANALYZE VERBOSE语句更新统计信息，并输出表的相关信息
analyze VERBOSE tpcds.customer_address;
–查看系统表中表的统计信息
select relname, relpages, reltuples from pg_class where relname = ‘customer_address’;
3.打印执行计划
–使用默认的打印格式
SET explain_perf_mode=normal;
–显示表简单查询的执行计划
EXPLAIN SELECT * FROM tpcds.customer_address;
–以JSON格式输出的执行计划（explain_perf_mode为normal时）
EXPLAIN(FORMAT JSON) SELECT * FROM tpcds.customer_address;
–禁止开销估计的执行计划
EXPLAIN(COSTS FALSE)SELECT * FROM tpcds.customer_address;
–带有聚集函数查询的执行计划
EXPLAIN SELECT SUM(ca_address_sk) FROM tpcds.customer_address WHERE ca_address_sk<100;
–有索引条件的执行计划
create index customer_address_idx on tpcds.customer_address(ca_address_sk);
EXPLAIN SELECT * FROM tpcds.customer_address WHERE ca_address_sk<100;
4.垃圾收集
–VACUUM回收表或B-Tree索引中已经删除的行所占据的存储空间
update tpcds.customer_address set ca_address_sk = ca_address_sk + 1 where ca_address_sk <100;
VACUUM (VERBOSE, ANALYZE) tpcds.customer_address;
5.事务日志检查点
–检查点（CHECKPOINT）是一个事务日志中的点，所有数据文件都在该点被更新以反映日志中的信息，所有数据文件都将被刷新到磁盘CHECKPOINT;
CHECKPOINT;
6.清理数据
drop schema tpcds cascade;
课后作业
1.创建分区表，并用generate_series(1,N)函数对表插入数据
2.收集表统计信息
-- 1.
create table store
(
c1 int,
c2 char(2)
)
partition by range (c1)
(
partition p0 values less than (10),
partition p1 values less than (20),
partition p2 values less than (30),
partition p3 values less than (40),
partition p4 values less than (50)
);
insert into store values(generate_series(0, 49));
-- 2.
select relname, relpages, reltuples from pg_class where relname = 'store';
analyze VERBOSE store;
select relname, relpages, reltuples from pg_class where relname = 'store';
3.显示简单查询的执行计划；建立索引并显示有索引条件的执行计划
-- 3.1.
SET explain_perf_mode=normal;
EXPLAIN SELECT * FROM store;
-- 3.2.
create index idx_store_c1 on store(c1);
EXPLAIN SELECT * FROM store WHERE c1<50;
4.更新表数据，并做垃圾收集
5.清理数据
-- 4.
update store set c1 = c1 - 1 where c1<100;
VACUUM (VERBOSE, ANALYZE) store;
-- 5.
drop table store;
学习心得
本节重点知识点：
EXPLAIN
CHECKPOINT
以及，复习第8节分区表相关内容。
参考文档
松鼠镇楼，按时打卡
